In many applications, it is desirable to fill a container with a heated material and to then seal the container while the material is still in a heated state so as to sterilize the product and package and make the product safe for consumption. For example, various types of beverages are packaged in “hot-fill” containers fabricated from polyethylene terephthalate (PET). Typically, such containers are filled and capped at temperatures around 185° F. A container can deform when exposed to a liquid that has been heated above the glass transition temperature (Tg) of the material from which the container is formed. Moreover, steam and/or other heated gas in a sealed container headspace will condense as the container contents cool. Headspace condensation produces a vacuum in sealed hot-filled containers.
Most hot-fill beverage containers are designed to operate at or near atmospheric pressure. If such a container has a significant internal vacuum after it is sealed, it will deform and may buckle upon cooling. To avoid such distortion, any internal pressure that is significantly lower than external atmospheric pressure should be minimized and/or the container provided with appropriate structural support. Various techniques have been developed in this regard. For example, some PET container designs include movable vacuum panels or movable bases. Some hot-fill beverage containers have a thicker wall construction. These features result in heavier PET containers and increased material cost, however. Other techniques also have various drawbacks. Accordingly, there remains a need for additional techniques and devices that can reduce and/or relieve vacuum generated by hot-filling of deformable containers.